The invention relates to a proportional magnet for a hydraulic directional control valve and to a method for the production thereof.
Directional control valves of this kind are used, for example, in internal combustion engines for the actuation of hydraulic camshaft adjusters.
DE 103 00 974 A1 discloses a proportional solenoid valve of a camshaft adjuster device for motor vehicles. The proportional solenoid valve has a valve housing in which a piston can slide and which has a plurality of connections via which hydraulic oil can be supplied. The proportional solenoid valve also comprises an electromagnet part with which the piston can be adjusted by means of a plunger. The plunger is mounted in an axial bore in a housing of the electromagnet part, as a result of which it can slide axially.
DE 102 11 467 A1 presents a camshaft adjuster having an electromagnet which is designed as a repelling proportional magnet. The proportional magnet has a magnet armature which is fixedly seated on an armature plunger which is guided through a pole core and which bears with a free end surface against a control piston or against a part fixedly connected thereto. The magnet housing and magnet flange are screw-connected to a control housing cover and sealed off by means of a flat sealing means.
DE 101 53 019 A1 describes an electromagnet which is suitable, in particular, as a proportional magnet for operating a hydraulic valve. The electromagnet comprises a hollow cylindrical coil former which is delimited by an upper pole shoe and a lower pole shoe. The electromagnet is surrounded by a magnet housing. The coil former acts magnetically on a magnet armature which transmits the magnetic force onward via a plunger rod for operating the hydraulic valve. The plunger rod is mounted in an axial bore in the lower pole shoe, as a result of which it can slide axially.
DE 10 2004 057 873 A1 relates to a seat valve having a line system for conducting an inflowing medium through it. The seat valve has a seat and an adjustable closing element in the line system. The adjustable closing element is operated by means of an electromagnetic actuating device. The electromagnetic actuating device comprises an armature housing in which an armature is arranged so as to be adjustable in the direction of a coil axis. The armature is connected to an actuating element which operates the closing element. The actuating element is mounted in an axial bore in the housing of the electromagnetic actuating device, as a result of which it can slide axially.
DE 10 2005 048 732 A1 relates to an electromagnetic actuating unit of a hydraulic directional control valve. The electromagnetic actuating unit comprises an armature, which is arranged within an armature chamber such that it can slide axially, and a pole core, which is arranged in a receptacle in the housing by means of a press fit and delimits the armature chamber in one movement direction of the armature. An armature guide sleeve is provided for axially guiding the armature. Furthermore, the electromagnetic actuating unit comprises a coil which is preferably encapsulated with a non-magnetizable material so as to form a coil former. The armature is mounted in a sliding sleeve, as a result of which it can slide axially with low friction.
JP 2005-188630 A describes a hydraulic directional control valve having an electromagnetic actuating unit. The electromagnetic actuating unit comprises a coil for generating a magnetic field which acts on an armature which can slide axially. The armature comprises an actuating element which operates the hydraulic directional control valve. The actuating element is mounted in an axial bore in the housing of the electromagnetic actuating device, as a result of which it can slide axially.
FIG. 1 shows a longitudinal sectional illustration of a further electromagnetic actuating unit according to the prior art. Said electromagnetic actuating unit is designed for actuating a hydraulic directional control valve which is designed as a central valve and which is arranged radially within an internal rotor of an apparatus for variably adjusting the control times of an internal combustion engine. The electromagnetic actuating unit comprises firstly a coil 01 which is fed electrically via a plug contact 02. The coil 01 is arranged within a coil former 03 which is produced by encapsulation of the coil 01 with a plastic. The magnetic field that can be generated by means of the coil 01 is transmitted via a soft-iron circuit, which comprises a yoke 04, a yoke disk 06, a pole core 07 and a housing 08, to a magnet armature 09 which is mounted such that it can move axially. The magnetic field exerts a magnetic force on the magnet armature 09 via an air gap between the pole core 07 and the magnet armature 09. Said magnetic force is transmitted via a pressure pin 11 of the magnet armature 09 to a piston of the central valve (not shown). The electromagnetic actuating unit is fastened by means of a flange 12 of the housing 08 to the central valve or to a housing surrounding the central valve. The magnetic field which can be generated by means of the coil 01 does not act entirely in the sliding direction of the magnet armature 09 on account of an eccentricity of the magnet armature 09. Said eccentricity is caused firstly by a degree of play of the magnet armature 09 and of the pressure pin 11 in the bearing arrangement thereof. Secondly, the eccentricity is a result of a deviation of the coaxiality between an armature bearing 13 and a pole core bearing 14. Said deviation may be extremely large depending on the assembly concept and on the tolerances of the components of the electromagnetic actuating unit. On account of the eccentricity of the magnet armature 09, parts of the magnetic field which can be generated by means of the coil 01 act laterally on the magnet armature 09, as a result of which forces are generated which act laterally on the magnet armature 09. Said laterally acting forces are proportional to the eccentricity of the magnet armature 09 or even proportional to the square of the eccentricity of the magnet armature 09. The alignment errors resulting from the deviation of the coaxiality between the armature bearing 13 and the pole core bearing 14 lead to tilting of the magnet armature 09 in its armature bearing 13. As a result of said tilting, the pressure pin 11 no longer slides on the entire bearing surface of the pole core bearing 14; in particular, a situation may arise in which the pressure pin 11 is mounted only on the edges of the pole core bearing 14. This leads to restricted functionality of the electromagnetic actuating unit and to increased wear of the pressure pin 11 and of the pole core bearing 14. Furthermore, the increased wear leads to an increasing eccentricity of the magnet armature 09, as a result of which the forces acting laterally on the magnet armature 09 increase yet further. As a result, the wear exhibits a progressive profile. The final result is failure of the apparatus for variably adjusting the control times of the internal combustion engine, in particular on account of the fact that the adjustment of the control times of the internal combustion engine can no longer take place within the admissible adjustment times.
New injection molding dies are always required for producing the known proportional magnets when variations in the magnet characteristics or stroke are desired or when other properties are intended to be changed in accordance with clients' requests.